Important information is often provided on documents, such as negotiable instruments, by imprinting transfer media in the form of visible indicia onto the face of the instrument. A common transfer medium is carbon which is transferred from a sheet of carbon paper placed over the face of the instrument, or ink from an inked typewriter ribbon. The transfer medium is imprinted onto the face of the instrument by typing, hand writing, mechanical means, etc. Such imprinted visible indicia is often subjected to unauthorized alteration. The negotiable instrument may be a bank check, money order, bill of exchange, certificate of deposit, treasury check, cashier's check, traveler's check, letter of credit, warrant, airline ticket, contract, deed, securities certificates, identification card, etc. Illegal alterations cause financial loss to the issuers resulting in costly legal action.
Several illicit practices have been commonly used to alter such instruments. For visible indicia formed by transferable ribbon, a pressure-sensitive tape has been used to lift the images. For indicia formed by carbon paper, inked ribbon, and ink pens, a combination of an eraser and a sharp-edged object has been used to alter the numbers. For indicia formed by special inks, organic solvents have been used to alter such indicia. So far, no known system can counter such illicit alterations.
Thus, there has been a continuing need for a tamper evident system useful for negotiable instruments and other valuable documents.